In recent years, semiconductor integrated devices (IC chips) used as microprocessors of computers or the like have been enhanced in speed and function more and more, and, thus, IC chips tend to have an increased number of terminals and a reduced inter-terminal pitch. In general, a large number of terminals are densely disposed in an array on the bottom face of an IC chip. Such a group of terminals are flip-chip connected to a group of terminals on the motherboard. However, since the inter-terminal pitch differs greatly between the IC chip side terminal group and the mother board side terminal group, difficulty is encountered in connecting the IC chip directly onto the motherboard. Therefore, in general, a semiconductor package including an IC chip mounted on an IC chip mounting wiring substrate is manufactured, and is then mounted on the motherboard.
A multilayer wiring substrate, in which buildup layers are formed on both of a surface and a reverse surface of a core substrate, is commercialized as an IC chip mounting wiring substrate forming such a kind of package. The multilayer wiring substrate employs, as a core substrate for instance, a resin substrate (glass epoxy substrate, etc.) formed with a resin-impregnated reinforcing fiber. And, the buildup layers are formed by stacking alternately resin insulating layers and conductor layers on a surface and a reverse surface of the core substrate having stiffness property. That is, in the multilayer wiring substrate, the core substrate serves to take a reinforcing role and is formed very thick as compared with the buildup layer. In addition, the core substrate is formed with wiring (in detail, through hole conductor, etc.) penetrated therein for electrically connecting the buildup layers formed on a surface and a reverse surface of the core substrate.
In recent years, signal frequencies used have been transferred to a high frequency band with high speed in a semiconductor device. In this case, the wiring penetrating the core substrate serves as a great inductor, causes transmission losses in high frequency signals or failures in circuit operations, and prevents the high speed. To solve such problems, a multilayer wiring substrate having no core substrate is disclosed (e.g., see Patent Document 1). Since the multilayer wiring substrate has no relatively thick core substrate to reduce the whole length of wiring, the transmission loss of the high frequency signal is reduced, thereby it is possible to operate a semiconductor integrated circuit device at a high speed.